There has been significant interest in apparatus and methods for identifying and verifying various articles or products (or objects) such as explosives, ammunition, paint, petroleum products, and documents. Known methods used to identify and verify such objects generally involve adding and detecting materials like microparticles, bulk chemical substances, and radioactive substances. Similar marking methods include inks that are transparent in visible light are sometimes applied to objects and the presence (or absence) of the ink is revealed by ultraviolet or infrared fluorescence. Other methods include implanting microscopic additives that can be detected optically. Other methods used for identifying and verifying objects include those described in U.S. Pat. Nos. 6,106,021, 6,082,775, 6,030,657, 6,024,200, 6,007,744, 6,005,915, 5,849,590, 5,760,394, 5,677,187, 5,474,937, 5,301,044, 5,208,630, 5,057,268, 4,862,143, 4,485,308, 4,445,225, 4,390,452, 4,363,965, 4,136,778, and 4,045,676, as well as European Patent Application Nos. 0911626 and 0911627, the disclosures of which are incorporated herein by reference.
As well, there has been significant interest in using similar methods to collect and record data about an object. In particular there has been significant interest to authenticate objects using these methods, e.g. to prevent loss or counterfeiting. Recognizing that manual data collection and keyed data entry were inefficient and error-prone, many industries adopted bar code technology in the mid 1980s. Bar codes were determined, however, to not be suitable for direct part (or object) marking (DPM). Instead, bar codes were used on labels or other packaging for the object or part.
To obtain direct part marking, many industries-together with U.S. governmental agencies—developed machine-readable two-dimensional (2-D) symbols designed to be applied to non-paper substrates. This development resulted in the data matrix symbol technologies that could be permanently applied to the materials or substrate of most products or objects without impacting performance. Additional DPM technologies quickly followed and were adopted by the automotive, electronics, pharmaceutical, and aircraft industries. These industries relied heavily on the use of mold, cast, or forge; engraving; electrical arc pencil; electrical-chemical marking; embossing; hot stamp; rubber ink stamp; stencil and silk screen; vibration-etch; and add-on tags for part identification.
These marking methods, originally designed to apply human-readable markings, did not successfully apply micro-size ({fraction (1/32)}-inch to {fraction (15/64)}-inch square), high-density machine-readable symbols. Their manual operations also added to the large number of data transposition errors. Thus, industries began to refine existing marking methods so they could be utilized to apply 2-D (e.g., data matrix) symbols. The manual metal stamp, vibro-etch, and embossing technique methods were replaced by dot peen machines. Automated micro-profilers were designed to replace the manual cutting wheel used to produce paint stencils. Photo stencils and thermal printing materials were developed to replace the direct impact electro-chemical marking stencil materials. Ink jet and adhesive dispensing machines were built to replace rubber stamps. Laser marking systems were designed to replace the electric-arc etch and hot stamp processes. See, for example, “Applying Data Matrix Identification Symbols on Aerospace Parts” NASA Technical Standard NASA-STD-6002A (November 2002) and “Application of Data Matrix Identification Symbols to Aerospace Parts Using Direct Part Marking Methods/Techniques” NASA Technical Handbook NASA-HDBK-6003A (November 2002), the disclosures of which are incorporated herein by reference.
Unfortunately, many of the non-DPM methods for identifying and authenticating objects are unsatisfactory for several reasons. First, they are often difficult and time-consuming. In many instances, a sample of the object (of the object itself) must be sent to an off-site laboratory for analysis. In other instances, the apparatus are often expensive, large, and difficult to operate. Finally, due to the unsophisticated nature of the methods, they could be easily duplicated and counterfeited, rendering them useful only in the use of routine unsecured identification and not particularly useful for authentication.
Yet 2D (data matrix) symbols are also unsatisfactory. They can be limited to two-dimensional structures or are limited because of the type of substrate/material used in the object or product. Data matrix symbols for automatic identification have evolved to the point that optically visible marks, especially those that appear as checkerboard bar codes on parts, are possible on any surface. Many of those surfaces (especially highly polished or smooth reflective ones), however, are not friendly to the optical scanner used to capture the image of the symbol and decode it.
It is also common to mark data matrix symbols on the surface of an item and have them imaged even though the symbols have been covered with paint or other coatings. Reading those symbols through the paint/coating is generally accomplished by two methods. The first method requires the addition of some constituent that can be imaged by a sensor, e.g., a magneto-optic scanner that can sense and image a symbol that has been backfilled with a magnetic material. See, for example, U.S. Pat. No. 5,742,036, the disclosure of which is incorporated herein by reference. The second method requires changing the substrate when applying the symbol to the extent that symbol data cells are either significantly higher or lower than the host substrate, making them detectable with ultrasonic means. See, for example, U.S. Pat. No. 5,773,811, the disclosure of which is incorporated by reference.
Both methods offer the ability to detect symbols that are securely hidden under a coating of paint. These methods, however, do not offer uniqueness to the extent that the symbol precludes counterfeiting. As well, these symbols can be detected and marked on duplicate products almost as easily as visible marks, rendering them useful only in routine unsecured identification and not particularly useful for authentication purposes.